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SubjectRe: [PATCH 0/20] return f_fsid for statfs(2)
On Jan 19, 2009  20:39 -0600, Dave Kleikamp wrote:
> On Tue, 2009-01-20 at 07:36 +0800, Andreas Dilger wrote:
> > The whole point of fsid (for NFS) is that this identifies the filesystem
> > over reboot, even if the block device ID changes, or if the filesystem
> > doesn't have a block device at all (e.g. cluster filesystem).
> I guess that just demonstrates how little I know about what the fsid is
> about. Would it be preferable for file systems that have a uuid to use
> that instead? Of course anything is an improvement over zeroes.

Yes, that is what the ext* patches do - fold the 128-bit UUID into a 64-bit
fsid so that it is constant across reboots. The chance of UUID collision
is about 1/2^32 due to birthday paradox, which is fairly low, and in case
this happens one of the filesystem UUIDs can be regenerated.

Cheers, Andreas
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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